Peel the peaches and core them. Then slice them up into chunks and place them into a saucepan. Sprinkle on the sugar, cornstarch, cinnamon, and lemon juice. Bring the mixture to a boil at medium heat and let it bubble for ten minutes. Use a masher to break up the peach chunks. Then turn the heat down to medium low and allow it to thicken up. Lastly, remove from the heat and stir in the whiskey.
SAGE SIMPLE SYRUP
Add equal parts of sugar and water with fresh sage leaves to a saucepan set over medium-high heat. Bring to a boil and stir to dissolve the sugar. Reduce heat for 10 minutes and simmer to steep. Then remove from the heat and cool to room temperature, about 30 minutes. Then pour into a jar, straining out the leaves with a fine mesh strainer.
BROWN SUGAR CAKE
Preheat your oven to 350 degrees F and butter up three 8 inch round cake pans. Line them with parchment rounds, if desired. Note that you can easily halve this recipe and make a smaller 6 inch layer cake using 6 inch cake pans instead.
Use a stand mixer equipped with the paddle attachment and beat your butter on medium speed for one minute. Scrape the bowl then add the brown sugar and continue beating for 5 more minutes. Then scrape the bowl again before adding the eggs one at a time, beating after each addition. Add the vanilla bean paste with the last egg. Turn the mixer to the lowest speed.
Meanwhile, sift together your remaining dry ingredients. Add half of the flour mixture to the batter.
Then add the buttermilk. Finish off with the dry ingredients. Divide the batter among the cake pans. Bake for 22-28 minutes, using a toothpick to check and see if they are done. Leave the cakes in the tins for ten minutes before turning them onto cooling racks to cool completely before filling and frosting.
SPICED MASCARPONE FROSTING
Use the whisk attachment of your stand mixer and a clean bowl for your frosting. Add the mascarpone, cream cheese, and butter. Begin whipping it on medium speed until it is smooth and free of lumps.
Then turn the mixer down to low while you add the powdered sugar since we aren’t ready for a blast of snow flurries to the face just yet. Once it is all incorporated add the bourbon and spices.Next, turn it up to medium high and whip for about 5 minutes, until it is fluffy, smooth, and fragrant.
PEACH, SAGE, AND WHISKEY LAYER CAKE ASSEMBLY
Begin by setting a dollop of frosting on a cake board to hold the cake in place. Then put the first layer onto that cake board. Brush on simple syrup.
Then spread on a thin layer of frosting, followed by piping out a ring around the edge to hold in the filling. Scoop in half of the peach filling and spread to the “frosting wall”. Then repeat with the next cake round. Finish with the third cake. Do brush on syrup onto the third cake round before covering the cake in a final layer of frosting.
This cake should be chilled until ready to eat. Take it out about an hour before serving.